Pressure sensitive adhesive composition which is water dispersible under alkaline pH conditions

Abstract

A pressure sensitive adhesive which is dispersible at an alkaline pH but not at an acidic or a neutral pH is disclosed. The adhesive is essentially free from plasticizers (i.e., it contains less than 0.1 part of plasticizer per part of polymer). The polymer is formed from A, B and C monomers. The A monomer is hydrophobic and is an acrylic or methacrylic ester of a non-tertiary C 2 -C 14 alcohol. It comprises from 50 to 80 weight % of the polymer. The B monomer contains β-carboxyethyl acrylate (BCEA) or a salt thereof or a mixture of BCEA or a salt thereof with a vinyl carboxylic acid or a salt thereof. The polymer contains from 10 to 30 weight % of B monomer. The acid groups of the polymer have been neutralized with from 0.5 to 2 equivalents of an alkali metal hydroxide. The C monomer is an X--Y--Z macromer. X is copolymerizable with the A and B monomers. Y is a divalent linking group. Z is a water dispersible group that contains at least two units which are essentially unreactive under free radical conditions used to form the polymer. C comprises from 10 to 30 weight % of the polymer.

We claim: 
     
       1. A pressure sensitive adhesive composition which is dispersible at an alkaline pH but not at an acidic or neutral pH, comprising (a) a polymer formed from A, B, and C monomers wherein A is a hydrophobic monomer selected from the group consisting of an acrylic or a methacrylic ester of a non-tertiary alcohol having from 2 to 14 carbon atoms, wherein A comprises from 50 to 80% by weight of A plus B plus C   B is a monomer which contains (1) β-carboxyethyl acrylate or a salt thereof, (2) a mixture of the β-carboxyethyl acrylate or the salt thereof and a vinyl carboxylic acid or a salt thereof other than the carboxyethyl acrylate or the salt of the carboxyethyl acrylate, wherein B comprises from 10 to 30% by weight of A plus B plus C, and wherein the carboxylic acid groups of said polymer have been neutralized with from about 0.5 to about 2 equivalents of an alkali metal hydroxide per carboxylic acid group, and wherein when the mixture of the β-carboxyethyl acrylate and the vinyl carboxylic acid is used, the β-carboxyethyl acrylate comprises at least 10% by weight of A plus B plus C, and   C is a water-dispersible macromolecular monomer which has the formula X--Y--Z wherein X is a moiety copolymerizable with A and B, Y is a divalent linking group which joins X to Z and Z is a water-dispersible group which contains at least two units which are essentially unreactive under free radical initiated copolymerization conditions used to form the polymer, and wherein C comprises from 10 to 30% by weight of A plus B plus C; and     (b) less than about 0.1 part of a plasticizer per part of said polymer.   
     
     
       2. The pressure sensitive adhesive of claim 1 wherein said carboxylic acid groups have been neutralized with from 0.75 to 1.5 equivalents of said alkali metal hydroxide per carboxylic acid group. 
     
     
       3. The pressure sensitive adhesive of claim 1 wherein said A monomer comprises from 60 to 75% by weight of A plus B plus C, said B monomer comprises from 10 to 20% by weight of A plus B plus C, and said C monomer comprises from 10 to 30% by weight of A plus B plus C. 
     
     
       4. The pressure sensitive adhesive of claim 1 wherein said B monomer is a mixture of β-carboxyethyl acrylate, acrylic acid, and acrylic acid oligomers. 
     
     
       5. The pressure sensitive adhesive of claim 1 wherein said C monomer has a weight average molecular weight in the range of 350 to 5,000. 
     
     
       6. The pressure sensitive adhesive of claim 5 wherein said C monomer has a weight average molecular weight in the range of 400 to 750. 
     
     
       7. The pressure sensitive adhesive of claim 5 wherein said C monomer has an inherent viscosity of from 0.7 to 1.5 dl/g in 2-butanone at 27.5° C. 
     
     
       8. A pressure sensitive adhesive tape comprising a layer of pressure sensitive adhesive of claim 1. 
     
     
       9. The pressure sensitive adhesive tape of claim 8 further comprising a supporting layer carrying said pressure sensitive adhesive layer on at least one surface thereof. 
     
     
       10. The pressure sensitive adhesive tape of claim 9 wherein said supporting layer is a release liner. 
     
     
       11. The pressure sensitive adhesive tape of claim 9 wherein said supporting layer and said pressure sensitive adhesive layer are anchored to one another. 
     
     
       12. The pressure sensitive adhesive tape of claim 11 wherein said supporting layer is dispersible at an alkaline pH. 
     
     
       13. The pressure sensitive adhesive tape of claim 11 wherein said supporting layer is polymeric. 
     
     
       14. The pressure sensitive adhesive tape of claim 13 wherein said polymeric layer is dispersible at an alkaline pH. 
     
     
       15. The pressure sensitive adhesive tape of claim 9 wherein said supporting layer carries said pressure sensitive adhesive on opposed surfaces thereof. 
     
     
       16. A fabric bearing a portion of the pressure sensitive adhesive tape of claim 8. 
     
     
       17. A fabric according to claim 16 in the form of a mammalian body covering. 
     
     
       18. A closure system comprising an article to be closed and a portion of the pressure sensitive adhesive tape of claim 8. 
     
     
       19. The pressure sensitive adhesive tape of claim 11 in the form of a sterilization indicator. 
     
     
       20. A polymer film bearing a portion of the pressure sensitive adhesive tape of claim 8. 
     
     
       21. A polymer film according to claim 20 in the form of a mammalian body covering.